<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>index</title>
    <style>
        body{
            background-color:gray;
        }
    </style>
</head>
<body>
    <div id="container">Zoom</div>
    <div id="zoomRatio"></div>
</body>
<script>
    document.getElementById("zoomRatio").innerHTML = window.innerHeight
    function getPageHeight(){
        let height = window.innerHeight;
        document.getElementById("zoomRatio").innerHTML = height;
        return height;
    }
</script>
</html>